Identification of Vasopressin‐Responsive Regulators of Aqp2 Gene Transcription

Abstract

The peptide hormone vasopressin regulates water excretion largely through control of the water channel protein, aquaporin‐2 (AQP2). Vasopressin regulates AQP2 in part by increasing Aqp2 gene transcription in collecting duct principal cells. Dysregulation of Aqp2 gene transcription has been implicated in a number of water balance disorders. However, how vasopressin regulates Aqp2 gene transcription is unclear. Here, we used next generation sequencing (NGS) techniques as well as prior published data to identify vasopressin‐responsive transcriptional regulators for Aqp2 gene transcription.CTCF is a DNA‐binding protein that homodimerizes with upstream or downstream DNA‐bound CTCF molecules to create ‘insulated loops'. Genes in these insulated loops are regulated mainly via enhancer or repressor interactions within the same loop. From the CTCF ChIP‐Seq database in mouse ENCODE, we found that three genes (Faim2, Aqp2 and Aqp5) are within the same insulated loop (99 kb‐length) defined by two strong CTCF‐binding sites. To identify regulatory elements for Aqp2 gene transcription in mpkCCD cells, we carried out ATAC‐Seq to identify genomic regions accessible to Tn5 transposase (analogous to DNase sensitivity footprinting). We identified 12 transposase‐accessible regions within the Faim2‐Aqp2‐Aqp5 insulated loop, which mark likely locations of enhancer or repressor elements controlling Aqp2 gene transcription.ChIP‐Seq was carried out for two candidate transcription factors, namely cyclic AMP‐responsive element‐binding protein (CREB) and CCAAT/Enhancer‐binding protein β (C/EBPβ) in mpkCCD cells. Vasopressin resulted in increased phosphorylation of CREB at Ser133, confirming a physiological response. Surprisingly, over multiple replicates, ChIP‐Seq identified no CREB‐binding sites within the Faim2‐Aqp2‐Aqp5 insulated loop, while CREB‐binding sites were found in the promoters of 29 transcription factors including AP‐1 transcription factors (Fos and Junb). The latter are recognized to play roles in regulation of Aqp2 gene transcription. In contrast, a strong C/EBPβ‐binding site was found just downstream from the Aqp2 gene within one of the transposase‐accessible regions identified by ATAC‐Seq. Vasopressin treatment increased C/EBPβ‐binding at this and other sites. Overall, the data are consistent with roles of C/EBPβ and CREB in regulation of Aqp2 gene transcription, although CREB effects are likely to be indirect through regulation of other transcription factor genes.This abstract is from the Experimental Biology 2018 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.